Rape (i.e., Brassica napus and Brassica campestris) is being grown as an increasingly important oilseed crop in many parts of the world. As a source of vegetable oil, it presently ranks behind only soybeans and palm and is virtually tied with sunflower for the number three position of commercial importance. The oil is used as both a cooking and salad oil throughout the world.
In its original form rapeseed oil was found to have deleterious effects on human health due to its relatively high level of erucic acid which commonly is present in native cultivars in concentrations of 30 to 50 percent by weight based upon the total fatty acid content. In the past plant scientists identified a germplasm source of low erucic acid rapeseed oil and began incorporating this trait into commercial cultivars. See, Chapter 6 entitled "The Development of Improved Rapeseed Cultivars" by B. R. Stefansson from "High and Low Erucic Acid Rapeseed Oils" edited by John K. G. Kramer, Frank D. Sauer, and Wallace J. Pigden, Academic Press Canada (1983).
In Canada plant scientists focused their efforts on creating so-called "double-low" varieties which were low in erucic acid in the oil and low in glucosinolates in the solid meal remaining after oil extraction (i.e., an erucic acid content of less than 2.0 percent by weight based upon the total fatty acid content, and a glucosinolate content of less than 30 micromoles per gram of the oil-free meal). These higher quality forms of rape developed in Canada are known as canola. In contrast European scientists worked to achieve only "single-low" types which were low in erucic acid, but did not attempt to improve the quality of the solid meal which retained a glucosinolate content of about 100 micromoles per gram of oil-free meal. The result of this major change in the fatty acid composition of rapeseed oil was to create an entirely new oil profile which often contained approximately 62 percent by weight of oleic acid based upon the total fatty acid content. Since the overall percentage of oil in the seed did not change appreciably when the new low erucic cultivars were developed, it appeared that the erucic acid had simply been redirected into other fatty acids with most becoming oleic acid. This level of oleic acid tended to vary within a fairly narrow range of approximately 55 to 65 percent by weight based upon the total fatty acid content. See, Chapter 7 entitled "The Introduction of Low Erucic Acid Rapeseed Varieties Into Canadian Production" by J. K. Daun from the previously identified Academic Press Canada (1983) publication. The weight percent of other fatty acids also varied somewhat, but not enough to define unique types with the potential for distinct uses or added commercial value. See, also "Prospects for the Development of Rapeseed (B. napus L.) With Improved Linoleic and Linolenic Acid Content" by N. N. Roy and A. W. Tarr, Plant Breeding, Vol. 98, Pages 89 to 96 (1987).
At the present time, canola oil is being marketed by Procter & Gamble under the Puritan trademark. Such vegetable oil typically is free of cholesterol, and the fatty acids present in it consist of approximately 6 percent saturated fatty acids in the form of stearic and palmitic acids, approximately 22 percent by weight linoleic acid which contains two double bonds per molecule of 18 carbon atoms, approximately 10 percent by weight alpha-linolenic acid which contains three double bonds per molecule of 18 carbon atoms, approximately 62 percent by weight oleic acid which contains a single double bond per molecule of 18 carbon atoms, and less than one percent by weight erucic acid which contains a single double bond per molecule of 22 carbon atoms.
Over the years scientists have attempted to improve the fatty acid profile for canola oil. For example, the oxidative stability of the vegetable oil is related to the number of double bonds in its fatty acids. That is molecules with several double bonds are recognized to be more unstable. Thus, scientists have attempted to reduce the content of alpha-linolenic acid in order to improve shelf life and oxidative stability, particularly under heat. This has not proved to be possible through the use of naturally occurring germplasm and the reported values for alpha-linolenic acid for such germplasm have been greater than 6 percent by weight (e.g., greater than 6 up to approximately 12 percent by weight). As reported by Gerhard Robbelen in Chapter 10 entitled "Changes and Limitations of Breeding for Improved Polyenic Fatty Acids Content in Rapeseed" from "Biotechnology for the Oils and Fats Industry" edited by Colin Ratledge, Peter Dawson, and James Rattray, American Oil Chemists' Society (1984), a mutagenesis experiment was able to achieve lines with less than approximately 3.5 percent by weight of alpha-linolenic acid based upon the total fatty acid content. The profiles of these lines indicate that nearly all of the alpha-linolenic fatty acid was being directed to linoleic acid and that the levels of oleic acid increased only one or two percent. Nevertheless the oil appeared to offer some advantages over normal canola oil. For instance, the refining process required less hydrogenation than normal canola oil and it exhibited a superior fry life.
In recent years studies have established the value of monounsaturated fatty acids as a dietary constituent. This has led to the popularization of the "Mediterranean Diet," with its emphasis on olive oil, a naturally occurring high source of oleic acid. Such a diet is thought to avoid the problem of arteriosclerosis that results from saturated fatty acids. Even in this diet, however, olive oil is thought to be less than ideal, due to its level of saturates. Canola oil is potentially a superior dietary oil, since it contains approximately one-half the saturated fats as olive oil, and since its relatively high levels of alpha-linolenic acid which are deleterious to shelf life and oxidative stability may be a benefit from a dietary point of view. Alpha-linolenic acid is believed to be a precursor for the synthesis by the body of a family of chemicals which may reduce risk from cardiovascular diseases.
It is recognized in the literature that the oleic acid content of canola varies slightly with the environment, temperature, and the moisture availability when the rapeseed is formed. As previously indicated the oleic acid content of available canola cultivars commonly is approximately 55 to 65 percent by weight. See, for instance, Table V at Page 171 from Chapter 7 entitled "The Introduction of Low Erucic Acid Rapeseed Varieties Into Canadian Production" by J. K. Daun appearing in "High and Low Erucic Acid Rapeseed Oils", Academic Press Canada (1983). As reported in the same article, rape varieties which possess greater concentrations of erucic acid will possess even lower oleic acid contents.
Occasionally higher oleic acid contents have been mentioned but have not been made available to the rapeseed grower. For instance, at Page 23 of proceedings of the 7th International Rapeseed Congress held at Poznan, Poland, on May 11 to 14, 1987, passing reference is reported to a canola sample having an oleic content of 79.0 percent under a given set of growing conditions and oleic acid content of 74 percent under different growing conditions. This plant was said to be produced by recurrent selection while employing unidentified parent plants. This is a non-enabling disclosure which will not place the reader of this publication in possession of a rape plant which produces rapeseeds having the increased oleic acid content.
As reported in U.S. Pat. Nos. 4,517,763; 4,658,084; and 4,658,085; and the publications identified therein, hybridization processes suitable for the production of rapeseed are known.
It is an object of the present invention to provide a substantially uniform assemblage of improved rapeseeds which yield a vegetable oil of increased stability.
It is an object of the present invention to provide a substantially uniform assemblage of improved rapeseeds which yield a vegetable oil of increased stability at elevated temperatures which particularly is suited for the deep-frying of food products for human consumption.
It is an object of the present invention to provide a substantially uniform assemblage of improved rapeseeds which yield a vegetable oil which possesses a higher oleic acid content than heretofore available in combination with other desirable traits.
It is an object of the present invention to provide in a preferred embodiment a substantially uniform assemblage of improved rapeseeds which yield a vegetable oil which possesses a higher oleic acid content in combination with a lower alpha-linolenic acid content than heretofore available.
It is another object of the present invention to provide a substantially uniform stand of rape plants capable upon self-pollination of forming rapeseeds which yield a vegetable oil of increased stability.
It is another object of the present invention to provide a substantially uniform stand of rape plants capable upon self-pollination of forming rapeseeds which yield a vegetable oil of increased stability which particularly is suited for the deep-frying of food products for human consumption.
It is another object of the present invention to provide a substantially uniform stand of rape plants capable upon self-pollination of forming rapeseeds which yield a vegetable oil which possesses a higher oleic acid content than heretofore available in combination with other desirable traits.
It is another object of the present invention to provide in a preferred embodiment a substantially uniform stand of rape plants capable upon self-pollination of forming rapeseeds which yield a vegetable oil which possesses a higher oleic acid content in combination with a lower alpha-linolenic acid content than heretofore available.
It is another object of the present invention to provide an improved vegetable oil derived from rapeseeds.
It is a further object of the present invention to provide a method for increasing the oleic acid content of rapeseeds and to thereby improve the stability of the vegetable oil derived therefrom.
These and other objects and advantages of the invention will be apparent to those skilled in the art from a reading of the following description and appended claims.